Workflow for texturing in games (in Unity)
I was struggling a lot with this topic two weeks ago aswell. And I had the same issue finding info on this topic. And while I haven't found a golden rule of thumb, I have found a workflow that works for me.
For my character, I made a 2048x2048 image split up in grids of 1024*1024 with a hard pixel line for use as a reference when placing the UV's.
Then I baked a 2048x2048 Ambient occlusion for each of my gridslots, in my case : Character Skin, Shirt/Vest, Pants, Accesoires, in which in each of the images only 1/4 of the space will be filled. I then combine those 4 maps in the correct order in the original 2048*2048 image in an image editor, save that, and reimport that in blender for each of your 4 slots.
All UV's will still be correctly aligned, and this allows me to paint/texture directly on the atlas, making any change to the character very easy and fast! My entire character, consisting of multiple objects is now mapped to 1 texture for the basecolor.
In your case for interior objects, I would make a similar grid but with more slots, maybe 4048x4048 divided by 4, bake/paint each object as you go along, and then add them to the atlas after each object is done.
It's a bit time intensive, but it gives you a lot of control over the process. If there is a better/faster way to do it, I would very much like to learn it too!